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Characteristics of a magneto-optical trap of molecules
摘要： We present the properties of a magneto-optical trap (MOT) of CaF molecules. We study the process of loading the MOT from a decelerated buffer-gas-cooled beam, and how best to slow this molecular beam in order to capture the most molecules. We determine how the number of molecules, the photon scattering rate, the oscillation frequency, damping constant, temperature, cloud size and lifetime depend on the key parameters of the MOT, especially the intensity and detuning of the main cooling laser. We compare our results to analytical and numerical models, to the properties of standard atomic MOTs, and to MOTs of SrF molecules. We load up to 2 × 10^4 molecules, and measure a maximum scattering rate of 2.5 × 10^6 s^?1 per molecule, a maximum oscillation frequency of 100 Hz, a maximum damping constant of 500 s^?1, and a minimum MOT rms radius of 1.5 mm. A minimum temperature of 730 μK is obtained by ramping down the laser intensity to low values. The lifetime, typically about 100 ms, is consistent with a leak out of the cooling cycle with a branching ratio of about 6 × 10^?6. The MOT has a capture velocity of about 11 m s^?1.
关键词： magneto-optical trap,ultracold molecules,laser-cooled molecules
更新于2025-09-23 15:21:01
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Synergic effect of pore size engineering and an applied electric field on the controlled permeation of alkali metal atoms and ions across pristine and defect-containing h-BN sheets
摘要： The permeation and selectivity of alkali metal atoms and ions through normal and defected hexagonal boron nitride was studied in the presence and absence of water and an electric field. The defects include one (VB & VN), two (VBN) and three atom (VN2B) vacancies. The morphology and size of the pore (defect) in the h-BN sheet significantly affect the energy barriers. These results indicate that an h-BN sheet with appropriate pore size possesses good Li/Li+ selectivity. The permeation of lithium atoms through VN2B-h-BN is almost a barrierless process (1.75 kcal mol?1). Moreover, the VBN h-BN nanosheet selectively allows the passage of Li atoms at room temperature with the highest selectivity ratio of 1.58 × 1013. The presence of water molecules increases the barrier of alkali metal atom permeation. The effect of water molecules is more pronounced for alkali metal atom permeation through a defected h-BN nanosheet as compared to alkali metal ions. An applied electric field perpendicular to the h-BN sheet further decreases the permeation barriers. For example, the energy barrier is reduced to 31 kcal mol?1 (from 34 kcal mol?1) in the presence of an electric field for the permeation of lithium through H2O–VB h-BN–H2O. These studies can be extended to investigate the separation capability of porous hexagonal boron nitride nanosheets for other metal atoms and ions.
关键词： electric field,permeation,water molecules,alkali metal atoms,hexagonal boron nitride,defects,ions,selectivity
更新于2025-09-23 15:21:01
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Strongly coupled evenly divided disks: a new compact and tunable platform for plasmonic Fano resonances
摘要： Plasmonic artificial molecules are promising platforms for linear and nonlinear optical modulation at various regimes including the visible, infrared and terahertz bands. Fano resonances in plasmonic artificial structures are widely used for controlling spectral lineshapes and tailoring of near-field and far-field optical response. Generation of a strong Fano resonance usually relies on strong plasmon coupling in densely packed plasmonic structures. Challenges in reproducible fabrication using conventional lithography significantly hinders the exploration of novel plasmonic nanostructures for strong Fano resonance. In this work, we propose a new class of plasmonic molecules with symmetric structure for Fano resonances, named evenly divided disk, which shows a strong Fano resonance due to the interference between a subradiant anti-bonding mode and a superradiant bonding mode. We successfully fabricated evenly divided disk structures with high reproducibility and with sub-20-nm gaps, using our recently developed sketch and peel lithography technique. The experimental spectra agree well with the calculated response, indicating the robustness of the Fano resonance for the evenly divided disk geometry. Control experiments reveal that the strength of the Fano resonance gradually increases when increasing the number of split parts on the disk from 3 to 8 individual segments. The Fano-resonant plasmonic molecules that can also be reliably defined by our unique fabrication approach open up new avenues for application and provide insight into the design of artificial molecules for controlling light-matter interactions.
关键词： sketch and peel lithography,artificial molecules,Fano resonance,plasmon coupling,tiny gap
更新于2025-09-23 15:21:01
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Cardanol and Guaiacol sourced Solution-Processable Green Small Molecules based Organic Solar Cells
摘要： An environment compatible organic solar cell (OSC) has potential to build a global clean energy infrastructure for the world. However, much less attention has been focused on the structures sourced from greener origin, to enhance the sustainability aspect of these devices. Herein, we report a rational design, synthesis and characterization of donor (D)-acceptor (A) based green organic small molecules, consisting of difluoro-2,1,3-benzothiadiazole (BTF2) as the acceptor, with a thiophene (T) and renewable resource materials, cardanol (C) and guaiacol (G) as the donor materials. The reference molecule, abbreviated as T4BTF2, is fully petro-sourced, while C2T2BTF2, G2T2BTF2 are partly renewable origin molecules. A broad and strong absorption characteristics ranging from 300 to 600 nm along with higher thermal stability is supportive for the utility of the greener origin small molecules in solar cells. Density Functional Theory (DFT) calculations revealed that G2T2BTF2 is highly planar than C2T2BTF2 due to the difference in the positioning of alkyl/alkoxy chain. Bulk heterojunction OSCs with PC71BM as the acceptor, G2T2BTF2 exhibited the high Voc of 0.83 V among all the analysed small molecules. When compared with the reference molecule T4BTF2, G2T2BTF2 showed a high PCE of 5.56 % with a high Jsc of 10.98 mA/cm2 and FF of 0.61, whereas the PCEs of T4BTF2 and C2T2BTF2 are 3.98 % and 3.23%, respectively. Our work demonstrates a rational approach to synthesize and develop green organic semiconductors using the bio-feedstock derived starting materials for realizing efficient and environment compatible OSCs.
关键词： Organic small-molecules,Green organic solar cells,Renewable phenols,fluorine substituents,Sustainable,donor-acceptor
更新于2025-09-23 15:21:01
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Inkjet printing a small-molecule binary emitting layer for organic light-emitting diodes
摘要： For inkjet-printed organic light-emitting diodes, it is critical to obtain a homogeneous small molecular-based emitting film. In contrast to the conventional strategy of utilizing mixed solvents, we have successfully inkjet printed a binary electrophosphorescent emitter with a single solvent. The binary emitter consists of a new host material of 3-(3,6-di-t-butylcarbazol-9-yl)-3'-(2-(4-t-butylphenyl)benzoimidazol-1-yl)-[1,1'-biphenyl], and an iridium complex dopant of bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate)- iridium(III) (Ir(MDQ)2(acac)). Compatible with Ir(MDQ)2(acac), the newly developed host is highly soluble and amorphous with a glass transition temperature of 137 oC upon cooling from the melt. The inkjet printability and film morphology of the emitting layer are strongly dependent both on substrates and the solvents. With the o-dichlorobenzene (o-DCB) as the single solvent, and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4?-(N-(p-butylphenyl))diphenylamine)] (TFB) as the hole transporting layer, a uniform emitter film morphology without any coffee ring is obtained. The phosphorescent OLEDs with the inkjet-printed emitter yields a maximum current efficiency of 17.89 cd/A, comparable to that of the Ir(MDQ)2(acac)?based OLEDs with spin-cast emitter.
关键词： Dewetting,Coffee ring,Inkjet printing,Phosphorescent OLEDs,Small molecules
更新于2025-09-23 15:21:01
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An extended chiral surface coordination network based on Ag <sub/>7</sub> -clusters
摘要： We present an extended metal-coordinated structure obtained by deposition of trimesic acid (TMA) onto the Ag(111) surface under ultra-high vacuum conditions followed by annealing to 510 K. Scanning tunneling microscopy and density functional theory calculations reveal the structure to consist of metal clusters containing seven Ag atoms each, coordinated by six dehydrogenated TMA molecules. The molecules are asymmetrically arranged, resulting in a chiral structure. The calculations confirm that this structure has a lower free energy under the experimental conditions than the hydrogen-bonded structures observed after annealing at lower temperatures. We show that the formation of such large metal clusters is possible due to the low adatom formation energy on silver and the relatively strong Ag-O bond in combination with a good lattice match between the structure and the Ag surface.
关键词： Ag7-clusters,TMA molecules,metal-coordinated structure,density functional theory,chiral structure
更新于2025-09-23 15:21:01
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Attosecond transient-absorption spectroscopy of polar molecules
摘要： We apply attosecond transient absorption spectroscopy (ATAS) to explore the effects of a nonzero permanent dipole on electron dynamics at the subfemtosecond scale, exemplified in the polar LiF molecule. In contrast with nonpolar systems, a familiar feature of the ATA spectra—the light-induced structures—are observed adjacent to a bright state. Moreover, a previously unobserved ladder structure is identified. The observations are analyzed in the context of a model based on fixed-nuclei adiabatic states, supported by full numerical simulations. Analytic calculations originating in the adiabatic model shed light on the nature and origins of the findings.
关键词： LiF molecule,attosecond transient absorption spectroscopy,electron dynamics,polar molecules,ladder structure,light-induced structures
更新于2025-09-23 15:21:01
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Carbazole/Benzimidazole-Based Bipolar Molecules as the Hosts for Phosphorescent and Thermally Activated Delayed Fluorescence Emitters for Efficient OLEDs
摘要： A series of carbazole/benzimidazole-based molecules, namely, o-CbzBiz, m-CbzBiz, and p-CbzBiz, were readily synthesized in three steps by integrating carbazole with benzimidazole via the ortho-, meta-, and para-positions of phenyl linked to N-phenyl carbazole. These bipolar molecules exhibited a maximum UV absorption band ranging from 310 to 327 nm and a maximum emission band ranging from 380 to 400 nm. Density functional theory calculations showed that the twist angles between the donor and acceptor moieties of these molecules were from 54.9 to 67.1°. Such a twisted structure hampered the π-electron conjugation within the molecule and resulted in high-lying LUMO levels and triplet energies, which make them suitable to be applied as host materials in OLED devices. Our results showed that a maximum external quantum efficiency (EQE) of OLED reached 21.8% when p-CbzBiz was applied as the host of a green phosphorescent emitter, i.e., Ir(ppy)2(acac). In addition, a maximum EQE of OLED reached 16.7% when o-CbzBiz with the host of a green TADF emitter, i.e., 4CzIPN. Moreover, these devices exhibited lower efficiency roll-off than the CBP-hosted device using the same emitters, which demonstrated the bipolar charge carrier property of carbazole/benzimidazole-based molecules.
关键词： thermally activated delayed fluorescence,bipolar molecules,phosphorescent,carbazole,OLEDs,benzimidazole
更新于2025-09-23 15:21:01
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Nonlinear Optics || Molecular Origin of the Nonlinear Optical Response
摘要： In Chapter 3, we presented a general quantum-mechanical theory of the nonlinear optical susceptibility. This calculation was based on time-dependent perturbation theory and led to explicit predictions for the complete frequency dependence of the linear and nonlinear optical susceptibilities. Unfortunately, however, these quantum-mechanical expressions are typically far too complicated to be of use for practical calculations. In this chapter we review some of the simpler approaches that have been implemented to develop an understanding of the nonlinear optical characteristics of various materials. Many of these approaches are based on understanding the optical properties at the molecular level. We also present brief descriptions of the nonlinear optical characteristics of conjugated polymers, chiral molecules, and liquid crystals.
关键词： chiral molecules,nonlinear optical susceptibility,liquid crystals,quantum-mechanical theory,conjugated polymers,time-dependent perturbation theory
更新于2025-09-23 15:21:01
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4H-pyranylidene-based small push-pull chromophores: Synthesis, structure, electronic properties and photovoltaic evaluation
摘要： The synthesis and electrochemical and optical characterizations of four new 4H-pyranylidene-based push-pull molecules are reported herein as well as their evaluation as donor materials for organic photovoltaics. Studied systems exhibit good absorption properties and appropriate LUMO levels for a photoinduced electron transfer to C60. Bilayer organic solar cells fabricated from these new donors and C60 as the acceptor gave photocurrent however with low power conversion efficiencies. As shown by X-ray diffraction and theoretical calculations, titled molecules present a twisted structure which may prevent the formation of suitable π-π contacts between adjacent molecules hence explaining their low photovoltaic performance.
关键词： Push-pull systems,Small conjugated molecules,4H-pyranylidene,Organic photovoltaics
更新于2025-09-23 15:21:01